9/16/2013 1:00 PM PDT

"Big Brother" star Britney Haynes -- who competed on the show in 2010 and 2012 -- has revealed her 2-month-old daughter has been diagnosed with cancer.

The 27-year-old reality star, along with her husband Ryan Godwin, broke the news on Facebook ... writing, "On September 1st, we were among the daily 720 sets of parents to be absolutely devastated with a Childhood Cancer diagnosis."

Britney's daughter, Tilly, was born on July 13.

Haynes continued, "Please take the time to pray for all these children, our sweet baby included. We appreciate each and every one."

Over the weekend, Britney tweeted a photo of Tilly -- writing, "Thank you for all of the thoughts, wishes, and prayers for my precious girl. She's everything to me."